semiminor axis

[ sem-ee-mahy-ner, sem-ahy-, sem-ee-, sem-ahy- ]
/ ˈsɛm iˈmaɪ nər, ˈsɛm aɪ-, ˌsɛm i-, ˌsɛm aɪ- /

noun

Geometry. one half the minor axis of an ellipse.
Astronomy. one half the minor axis of the ellipse that one celestial body describes around another, as a planet around the sun.

Origin of semiminor axis

First recorded in 1925–30; semi- + minor